That discordant duet you can hear comes from Victoria, where two strapping lads are serenading the Australian Greens. Riding high in the polls with the election two weeks away, they've got the Premier saving forests and the Opposition leader spruiking public transport.

It's all about the major parties 'wooing' the minor one to 'secure' their 'vital preferences'. It's also part of an enduring myth of contemporary Australian politics.

Preferences from Green votes will almost certainly decide some Victorian seats. Morgan and Newspoll have the Greens on 7 per cent support and Saulwick gives them 12. If the pollsters are right that could mean many seats will go to preferences.

But the myth lies in the belief that there is much Bob Brown, local Green apparatchiks or anyone else can do to influence the flow.

You wouldn't know it from the commentary, but 'above the line' voting (where a voter lets their chosen party decide preference allocation) is not an option at lower house elections. We fill in the squares ourselves. At Victorian and federal ones, compulsory preferential means you must number every box.

Many Australians slavishly follow how to vote cards, but few of them are Greens voters.

At last year's House of Representatives election the Greens received a record 5 per cent vote. Analysis by the Parliament House library, Canberra, showed that 74.83 per cent of their preferences flowed to Labor; 25 per cent to the Coalition.

But the boost to Labor in seats where the Greens preferenced them was miniscule, an average of just 3.5 per cent - of the Green vote.

The Australian Democrats, with similar support, two thirds of which flowed to Labor, wielded a bigger preference stick, their corresponding figure being 6 per cent.

To get an idea of this, imagine an electorate in which the Green candidate gets 10 per cent. The advantage to Labor of 'securing Green preferences' would, on average, be 0.35 per cent of the vote! Such an amount would make a difference in the tightest of seats only.

The Greens' dizzying new heights have little to do with the environment and everything to do with fuzzy Labor product differentiation. Simon Crean is seen as being too much like John Howard; Steve Bracks as being like Jeff Kennett.

Voting Greens, however, is one thing; registering a de facto vote for the Coalition is another entirely.

Leakage from the centre would be catastrophic for Labor under first past the post voting as the Brits have. And it may trouble Bob Carr in NSW in March next year under optional preferential.

But come November 30 the great bulk of Green votes will wash through to what they were anyway in all but name - Labor ones.

Peter Brent is editor of mumble.com.au, a website that looks at electoral behaviour.